Size press coating paper with tio2-starch paste to improve opacity



Dec. 8., 1970 o, WARE ETAL 3,545,066

. SIZE PRESS COATING PABER WITH T1 O3-STARCH PASTE TO IMPROVE OPACITY Filed Nov. 1, 1967 I FuRNIs'H FORMATION J ERSION OF I (REDUCE o PIGMENZL'IL'JQIQYIN SIZIE HIGH ENERGY COOKING WEB FORMATION E OF PIGMENTED SIZING SLURRY DRYING SIZE PRES COATING DRYING PAPER OF IM PROI/ED OPACITY/ T502 RATIO INVENTORS FRANKLYN O. WARE WILBUR W- KRUEGER CHARLES L. SOUKUP ATTORNEY United States Patent Office 3,546,066 SIZE PRESS COATING PAPER WITH TiO -STARCH PASTE TO IMPROVE OPACITY Franklyn O. Ware, Appleton, and Charles L. Soukup and Wilbur W. Krueger, Wausau, Wis., assignors by direct and mesne assignments, to Paper Production Aids, Inc., a corporation of Wisconsin Filed Nov. 1, 1967, Ser. No. 679,706 Int. Cl. D21d 3/00 US. Cl. 162-175 8 Claims ABSTRACT OF THE DISCLOSURE Opacity increases in paper achieved by the addition of titanium dioxide are improved by adding at least a portion of tht titanium dioxide to the paper as a sizing coating comprising starch and a stable suspension of titanium dioxide therein produced by cooking an aqueous mixture comprising starch and titanium dioxide with steam at a temperature above 212 F. While subjecting the mixture to mechanical energy in excess of that provided by the steam required to cook the mixture at the selected temperature.

BACKGROUND OF INVENTION Field of invention This invention relates to a method for opacifying paper with titanium dioxide and to novel size press coated papers produced thereby.

Description of prior art This invention is directed to the production of papers in which opacity is a problem, i.e., those of a weight such that the cellulose fibers forming the paper and any sizing coating thereon do not render the paper optimally opaque for their intended end use.

A large class of such papers are the printing grade papers. In these papers, opacity is integrally related to the weight and quality of the paper. Two examples of this class of paper are medium Weight printing papers, e.g., offset grade in the 40-120 lb. 25 weight range and light weight opacified papers, e.g., onionskin and airmail stationery papers, and register bonds whose weight range is from 9-16 lb. (17 or 23 to 40 1b., calculated as a 25 x ream. In these broad classes of papers, titanium dioxide is conventionally employed in the furnish as an opacifying agent. A substantial loss of titanium dioxide is experienced by this method because the titanium dioxide which is not retained in the formed web, which often amounts to 40 percent or more of the titanium dioxide supplied to the furnish, when recovered has only a small percentage of the opacifying capacity of the original titanium dioxide. The amount of titanium dioxide employed in the furnish ranges widely, e.g., from 25 to 400 lbs. per

3,546,066 Patented Dec. 8, 1970 ton of fiber, depending upon the target opacity and brightness and the type of fiber employed. Because titanium dioxide is an expensive additive for paper, there has been a continuing effort in the industry to achieve target opacities employing the least amount of titanium dioxide possible.

Irrespective of the amount of titanium dioxide added to the furnish, there are limits to the increase in opacity over that of the base sheet which can be achieved by its addition thereto. For example, with a 50 lb. Offset Printing grade paper having a 78 percent base sheet brightness, an 89 percent (Bausch and Lomb) opacity can easily be achieved by the addition of titanium dioxide to the furnish. A 91 percent opacity is a considerably more difiicult opacity to achieve for paper of this same weight and brightness and requires the addition of considerably more titanium dioxide, e.g., 100 lbs., to the Wet end. A 93 percent (B & L) opacity is about the maximum value which can be achieved for this type of paper by the addition of titanium dioxide to the furnish.

Similarly, with a lb. sheet, Offset Printing grade, having a 79 percent base sheet brightness, 90 percent opacity is easily achieved by the addition of titanium dioxide to the furnish. Here, the additional weight of the base sheet helps to achieve an additional point of opacity. A diflicult opacity to achieve for this paper would be 94 percent and 95 percent opacity is about the limit. With lb. sheet of the same quality and brightness in the range of 78-80 percent (G.E.), 95 percent opacity can be reached with the base sheet alone.

Generally speaking, opacity can be increased up to three points above the base sheet opacity by the wet end addition of about 20 lbs. per ton titanium dioxide per point of increased opacity desired. Attempts to achieve higher opacity increases becomes increasingly more expensive because much greater amounts of titanium dioxide are required. Finally, a point is reached Where even the addition of unlimited titanium dioxide to the furnish would not further increase the finished sheet opacity because the web cannot retain any more titanium dioxide.

In conjunction with the mechanics of wet end retention of titanium dioxide, according to the Kubelka-Munk Theory, an accepted theory in the paper industry, the higher the GE. brightness of the sheet, the less will be the opacity of the sheet, all other conditions being equal. This means it is harder to increase the opacity of a sheet having a high, e.g., percent (G.E.), brightness than a sheet having a relatively low, e.g., 78 percent, brightness. Consequently, it is very difiicult to produce uncoated papers having both high opacity and high brightness. It is in this area, i.e., the production of paper having both high brightness and high opacity, where the benefits of the present invention are the greatest.

Another factor related to sheet brightness is shade. Shade refers to the tint or color of the sheet. Sheets tinted cream or yellow are notoriously difficult to opacify. This difficulty is associated with the mechanics of measuring opacity. Contrary to the brightness theory, a cream tinted sheet of 75% brightness is as hard to Opacity as a 90 percent brightness blue-white sheet. In the production of tinted sheets which are difiicult to opacify, the economic advantages of the present invention are also high.

Another area where the present invention is of considerable value is in the area of light weight opacified papers, i.e., those commonly referred to as register bonds. A considerable market exists for this type of sheet in continuous forms work where customers woulr prefer to use a lighter weight sheet having the opacity of a heavier sheet. Such a market for such light weight papers is in the field of periodicals where considerable savings in mailing costs are effected if the desired opacity can be achieved with a lighter weight paper.

It is in these areas where the advantages of the present invention are most readily realized and it is in these areas that the present invention preferably pertains.

In some uncoated papers, e.g., cardboard, the base sheet is suffiiiently heavy to render the paper virtually or completely opaque. It is therefore unnecessary to employ an opacifying agent to increase their opacity. Coated papers are another broad class of papers which are highly opaque, irrespective of the opacity of the base sheet, because the coating is very heavy, e.g., 8-15 lbs./ream/side. In others, translucence rather than opacity is the desired property. This invention, at least the opacifying-improving aspect of it, is not therefore directed to these classes of papers because with them opacity is not a problem.

Titanium dioxide and other pigments have previously been also applied to paper as an ingredient of a coating for the paper, mainly in the production of coated papers. See, for example, US. 1,936,152, 2,106,709 and 2,360,- 828. A variety of methods have been employed to improve the results achieved in so doing. See, e.g., 2,032,211, 2,185,859, 2,216,143, 2,229,620, 2,229,621, 2,237,068, 3,041,200 and 3,115,438. Many techniques have been employed in an attempt to improve the pigmented mixture. See, e.g., 1,261,135, 1,733,524, 1,900,235, 2,140,394, 2,360,828, 2,388,526, 2,394,233, 2,526,598, 2,639,268, 2,849,326, 2,964,403, 3,307,975, and 3,308,037.

None of the inventions described above has resulted in the use of titanium dioxide or other opacifying agent in a sizing solution to increase the opacity of the base sheet because the amount applied in this manner heretofore has not significantly increased base sheet opacity. Heretofore, when pigmented size solutions were used, only a half-point or less improvement was noted.

Only when a coated paper is produced, i.e., by the application of at least 8 lbs./ream/side of pigment-containing solids, is opacity of the sheet significantly affected. When these coating weights are reached, the opacity of the coating itself becomes a significant factor because of the thickness of the coat. However, with the light weight coats produced by size coating with a pigmented sizing solution, no significant opacity improvement was achieved.

Thus, in the paper industry for many years efforts in improving opacity with titanium dioxide has been directed primarily toward improving the opacity increase achieved by its addition at the wet-end.

SUMMARY OF INVENTION According to this invention, at least a substantial portion of the titanium dioxide conventionally added to the furnish to increase the opacity of the base sheet is replaced by a lesser amount thereof applied as a size coat from a sizing paste containing the titanium dioxide in stable, highly dispersed form.

OBJECTS OF THE INVENTION It is an object of this invention to provide a method for increasing the opacity achieved by the addition of titanium dioxide to paper as an opacifying agent. Another object is the provision of a process for producing papers opacified with titanium dioxide to a level heretofore achieved only with papers of heavier weight. Still another object is the provision of a process for the production of papers having high brightness and opacity employing less titanium dioxide than heretofore possible. A further object is the provision of novel papers produced by the aforesaid processes. Other objects will be apparent to those skilled in the art to which this invention pertains.

DESCRIPTION OF THE INVENTION The following is a description of the manner of making and using and the best mode contemplated for carrying out the invention.

In the process of this invention, paper is opacified with titanium dioxide by employing at least a substantial portion of the titanium dioxide which is conventionally supplied to the furnish in the form of a pigmented sizing coating in which the titanium dioxide is unformly suspended in particulate, finely dispersed form, substantially free from the titanium dioxide agglomerates normally present when titanium dioxide is mixed with the sizing material in a conventional manner, thereby producing paper having an opacity greater than that of comparable paper produced by conventional means in which a comparable amount of titanium dioxide is supplied to the furnish only. Thus, in the process of this invention, the ratio of the increase in base sheet opacity to the TiO required to achieve this increase is higher than that realized in conventional processes.

SIZING PASTE The sizing paste employed in the process of this invention is titanium dioxide-containing pigmented paste which is used to surface-size the base sheet, i.e., provide the base sheet with a pigmented size coating. Any form of pigment grade titanium dioxide may be used. Its concentration in the sizing paste will depend on the amount required to achieve target opacity and brightness and the size pick-up achieved. Generally, it will constitute about 4 to 15 percent of the total solids when other pigments are present and up to 50 percent when used in the absence of other pigments.

The sizing colloids used to form the size coating usually will consist of or at least comprise starch, e.g., derived from corn, sorghum, potatoes, wheat, rice, tapioca, etc., with pearl starch being preferred because of cost. Modified starches, e.g., oxidized, enzyme converted, phosphated, sulfated, hydroxyethylated, acetylated, can be used as in conventional sizing formulations.

In addition to the titanium dioxide, other pigments can be included in the paste, e.g., alumina, the clays, including kaolin, especially those fractionated to improve brightness, talc, diatomite, calcium carbonate, e.g., chalk, magnesium carbonate, and mixtures of calcium and magnesium carbonate, barytes, raffold, calcium sulfite, calcium sulfate, blanc fixe, titanium calcium pigment, lithopone, titanated lithopone, etc. Because most of these are substantially cheaper than titanium dioxide, one or more, e.g., kaolin, alumina, are used in combinaion with the titanium dioxide and usually in substantially larger amounts, e.g., from 10 to 150 lbs/ton, preferably about 50 to lbs/ton.

The pigmented size paste is usually formed at a higher solids concentration than that conventionally employed because of the presence of the pigment solids as well as the sizing colloid. Total solids content will ordinarily range from about ten to 40 percent, of which about half to three-quarters will be sizing colloids.

The advantages of this invention are not achieved merely by blending titanium dioxide with the sizing slurry or sizing paste in a conventional manner. Specific means must be employed for dispersing the titanium dioxide in highly particulate, form so that the sizing paste is substantially free from agglomerated titanium dioxide. Generally speaking, sizing pastes will contain titanium dioxide agglomerates irrespective of whether the titanium dioxide is mixed with the sizing material before or after cooking. Moreover, they are unstable even at low solids, i.e., the titanium dioxide and other insoluble solids dispersed therein will precipitate if the sizing paste is not continuously stirred. Even those sizing pastes prepared so carefully that the titanium dioxide is in stable suspension conventionally contain such a large amount of titanium dioxide agglomerates that it cannot be used in the process of this invention.

A titanium dioxide pigmented sizing paste suitable for use in the process of this invention can be prepared by instantaneously cooking the sizing material according to the procedure described in U.S. Pat. 3,211,564, at high temperatures, e.g., 220 F. to 350 F., while simultaneously subjecting the slurry to an extremely high shearing force or other form of mechanical energy which rapidly disrupts the physical form of the uncooked hydrophillic colloid employed as the sizing material during the instantaneous cooking operation.

A useful method for preparing a sizing paste containing TiO suitable for use in the process of this invention is to heat a sizing slurry containing the TiO to above 212 F. using excess steam to provide the requisite shearing force. This can be accomplished in the cooking apparatus of U.S. 3,211,564 or 3,133,836 in the manner described in U.S. Pat. 3,133,836, i.e., using steam in excess of that required to bring the slurry to the selected cooking temperature. Because the slurry mixes with the steam as they both pass through a highly restricted orifice or orifices, the excess steam and slurry are mixed at extremely high velocities, thereby imparting the requisite mechanical energy to uniformly disperse the titanium dioxide particles in separated particulate, stable form in the cooked size paste. The greater the excess steam employed, the greater the mechanical and excess heat energy available for achieving this stable dispersion of the titanium dioxide particles. Cooking temperature is above 212 F., e.g., 225 to 375 F., preferably 300 to 350 F. The excess steam employed is preferably 2.5 to 5 times, most preferably about 3 times, the amount required to heat the slurry to the .selected cooking temperature.

Equipment which has been used to subject a sizing slurry to a high shearing force provided by mechanical means is disclosed in U.S. Pats. 2,526,598 and 2,717,213. High mechanical energy can also be provided with an ultrasonic disintegrator, e.g., the Branson Sonifier (Heat Systems Co., 60 Broad Hollow Road, Melville, N.Y.). Adding air, heated to a temperature which offsets the cooling effect by evaporation of the water in the slurry, to the steam employed in U.S. 3,211,564 will increase the velocity of sizing slurry through the orifices of the cooking apparatus, thereby providing a higher shearing force. Compressed air instead of steam, if heated sufiiciently to provide the requisite heat to bring the slurry to the desired cooking temperature, will also increase the shearing force achieved in the apparatus of 3,211,564.

As is apparent from the above, the most convenient method for forming the pigmented sizing paste used in the process of this invention is to cook the sizing colloids in the manner described above in the presence of the pigments, i.e., blend the pigments with the uncooked starch or other sizing colloid and then cook the resulting pigmented slurry. However, so long as the titanium dioxide, and preferably all the pigments, is dispersed in a colloid in the manner described above to produce a stable, uniform dispersion of the titanium dioxide particles, the resulting dispersion can thereafter be mixed with starch paste cooked in the same manner or conventionally in an unpressurized cooker. A further alternative is to blend the titanium dioxide and any other pigments with already cooked sizing paste and pass the mixture through an instantaneous cooker as described in 3,211,564 or 3,133,836

while subjecting the mixture to high mechanical energy, thereby producing a uniform stable dispersion of the pigment particles in the twice-cooked sizing colloid solution.

BASE SHEET FORMATION As stated above, the fibers used to produce paper according to this invention are those conventionally employed. Preferred are those used in the production of papers the opacity of whose base sheet is less than percent, especially those whose opacity is within the range of 70 and 90. Particularly preferred are cellulose fibers used to produce the high grade printing quality papers, e.g., offset bond, and the light weight opaque papers, e.g., register bonds, onionskin and airmail stationery grades. Although the furnish can contain a tinting pigment or dyestuif, preferred furnishes are those which produce the white, i.e., untinted, papers. All other ingredients conventionally employed in the formation of these grades of paper may be present in the furnish, e.g., rosin, alum, Waxes, sodium silicate, glues, casein, synthetic resins, etc. The only significant difference in the composition of the furnish used in the process of this invention is the amount of opacifying agent present therein. The amount of opacifying agent present, in this case titanium dioxide, will be substantially less, e.g., 10 percent less, usually 25 and often 50 percent less, than that normally present in the furnish used to prepare any specific grade of paper of comparable opacity. The difference between the amount conventionally employed and that employed in the process of this invention is inversely proportional to the opacity of the base sheet in the absence of any opacifying agent and also to the increase in opacity above base sheet opacity which is desired in the final paper. When the opacity of the base sheet is high, e.g., 90 percent or higher, when a relatively heavy size coating is applied, e.g., 25 to 50 lbs./ ton, or when only a small increase in base sheet opacity is desired, titanium dioxide sometimes can be omitted completely from the furnish. When the opacity of the unpigmented base sheet is less than 85, e.g., 80 or less, the difference in titanium dioxide which must be present in the furnish according to conventional techniques and by the process of this invention is greater and increases rapid- 1y as lighter and lighter Weight base sheets are produced. In the preferred aspects of this invention, the furnish contain less than half the titanium dioxide normally present therein when producing printing grade papers.

The web is formed and dried employing conventional techniques. Preferred weights range from light weight opaque papers, e.g., 23 to 40 lb. (25 or 9-16 lb. on a 17 X 5 basis, to lb. (25 X printing grades. Of the conventional printing grade weights, preferred are the 40-90 and especially preferred are the 50- 80 lb. weights.

SIZE COATING The most significant change in the technique employed to make the web is the use of a pigmented sizing solution. This solution can be applied to one or both of the sides of the at least partially dried sheet in any conventional manner, e.g., using a size press, which applied a size press coating of 1 to 100, e.g., 5 to 50, preferably 10 to 30 lbs./ton of titanium dioxide. In all other respects, the paper making techniques employed are substantially those conventionally employed for the production of tub-size or size press coated papers.

In addition to the savings achieved by the reduction and sometimes elimination of titanium dioxide from the wet end, which markedly reduces or eliminates titanium dioxide loss due to incomplete retention thereof in the web, and the savings resulting from the use of less titanium dioxide in order to achieve any selected opacity, numerous other advantages result in the practice of the process of this invention. For example, target specifications can more readily and more rapidly be achieved because opacity can be altered by regulating solids pick-up of the size press coating. This can substantially reduce the amount of broke produced in mill. Also, papers of substantially different opacity can be made in the same run rfom the same furnish. Also, papers with specifications heretofore unachievable can also be produced. Other advantages are lower base sheet weights required to achieve any minimum desired opacity.

A preferred aspect of this invention is printing grade papers whose opacity is at least 3 points above the base sheet opacity and contains less than 15 lbs. per ton TiO per point of opacity of the final sheet above base sheet opacity, preferably less than 10 lbs. per ton per point, a total of less than 50 lbs/ton, e.g., l30 lbs/ton, of titanium dioxide in a size press coating, and an opacity of at least 90, preferably untinted paper of less than 80 lb. (25 X /5o0) weight and a brightness of at least 90, at least 7 points of whose opacity is provided by a size press coating.

PIGMENT SIZE COATED PRINTING GRADE PAPERS The product aspect of this invention is directed primarily to the novel printing grade, i.e., book grade, paper having an unique opacity and brightness for any particular weight and grade and titanium dioxide content. These papers ordinarily are in the to 120 lb. 38/500) weight class, preferably less than 90 lb. weight. They are characterized by:

(a) Containing substantially less titanium dioxide in the base sheet, e.g., less than 75 percent and preferably less than half that present in conventional paper of the same grade, weight, brightness and opacity;

(b) A pigmented size coating containing up to 50 lbs/ton titanium dioxide, preferably 10 to lbs/ton;

(c) Optionally, the presence of other pigments in the size coating in amounts of up to 150 lbs./ton, usually about 50 to 100 lbs/ton;

(d) A total titanium dioxide content substantially less, e.g., 10 to 75 percent less, than the amount ordinarily present in conventional paper of the same grade, weight, brightness and opacity; and

(e) A surface which by electronmicrograph has a substantially higher substantially discrete, i.e., nonagglomerated, pigment particle count than that present in conventionally prepared paper of the same grade, weight, brightness and opacity.

With respect to the latter, electronmicrographs of the novel papers show fewer large agglomerates consisting of dozens to hundreds of titanium dioxide particles and substantially more such particles in substantially discrete form, i.e., containing 25 or less particles per grouping. Also, since the novel papers are often and preferably formed using a sizing paste containing other pigments in addition to the titanium dioxide, these particles can be seen in substantially higher concentration than in paper prepared by conventional means.

The above description of this invention has been limited to the production of titanium dioxide-containing papers. In certain instances, following the process of this invention it is possible to eliminate titanium dioxide completely from the paper, using only cheaper pigments to achieve the requiste brightness and opacity. This can be done when target brightness and opacity can be achieved by conventional means using pigments comprising less than about 75 lbs./ton of titanium dioxide, e.g., 50 lbs. or less per ton. In these papers, total pigment content is relatively high, e.g., 300 or more lbs./ton, usually about 350 to 450 lbs/ton. Ordinarily target opacity must be no greater than 90 (B & L) and usually no greater than 85, for papers of less than 100 lb. (25X 38/500) weight, in order to achieve it without the use of titanium dioxide. Brightness will ordinarily range from 75 to 90. Thus, for printing grade papers in the weight range of 40 to 90 lbs. (25 38/500), where an opacity of from 85 to 95 with a brightness of from to could be achieved by conventional means using from 300 to 40.0 lbs./ton pigments which required the presence of some but no more than 75 lbs./ton titanium dioxide, it is possible according to this invention to achieve these specifications without using titanium dioxide using a sizing paste described herein containing only brightening pigments, e.g., alumina and/or kaolin. This is a very surprising result because such pigments have heretofore had no significant effect upon base sheet opacity unless used to produce a coated paper.

With reference to the drawing, there is shown a flow sheet of a preferred method of performing the process of this invention.

The following are specific embodiments of this invention which are illustrative of but do not define the limits thereof.

EXAMPLE AfiSIZE PASTE FORMATION Pigmented sizing slurries of the compositions set forth in the examples which follow were prepared employing a commercially produced cooker (Penick and Ford) described in US. 3,133,836. The materials to be cooked were slurried together at solids ranging from 40 to 60 percent. These high solids slurries were then pumped through the Penick and Ford cooker at a slurry flow rate of 10 to 25 gallons per minute. The adhesive portion of the slurry was cooked instantly and continuously at temperatures of 310 to 330 F. and under pressures of 70 to 90 p.s.i.g. The instantaneous high-shear cooking caused the pigment portion of the cook to be thoroughly dispersed in the adhesive phase. After the instantaneous cooking, the sizing paste was diluted continuously with water to the desired total solids. The cooked paste was held in a holding tank until used. The titanium dioxide was stable in the sizing paste and showed no tendency to settle. Microscopic examination reveals a remarkable absence of the numerous titanium dioxide agglomerates normally present when it is blended, before or after cooking, with the hydrophylic colloid used as sizing material.

EXAMPLE B-SIZE COATED PRINTING PAPER PRODUCTION In the following examples, all runs were on a conventional Fourdrinier paper making machine equipped with a vertical or canted nip size press.

IV.-In these runs, the objective was to duplicate brightness and opacity of uncoated vellum finish, offset grade bond of 50, 60, 70, 80 and lb. paper produced from furnish of the following composition and sized with 12-14 percent oxidized starch, 120-140 lbs/ton pickup.

Furnish Sulfite 60 percent Kraft 40 percent Alum ca. 35 lbs./ton Rosin ca. 35 lbs/ton Alumina (hydral) 200 lbs./ton TiO (slurry) 230 lbs/ton TiO (beater) 50 lbs./ton

In the new furnish composition, the TiO at the beater was eliminated and at the slurry it was reduced to lbs/ton. Retention of the TiO at the wet end was 52.4, 56.4, 53.3 and 63.5 percent, respectively, for the 50, 60, 70, and 80 lb. papers. A pigmented sizing paste, produced in the manner described in Example A, of the following composition was applied to the dry base sheet.

50 parts Ultra White fractionated kaolin 25 parts alumina SD.

25 parts TiO [M] micronized anatase 50 parts hydroxyethyl starch (Penford 230) 50 parts native corn starch (Pearl X) The size Was applied at a 20-22 percent solids concentration.

Runs

I II III IV V a. b. a. b. a. b. a. b. a. b.

New Old New Old New Old New Old New Old Basis wt. lbs., 25x38/500 50. 3 50 61. 8 60 71. 3 70 80. 5 80 119. 120

Caliper, in. 10- 30 40 48 48 56 56 66 64 Q9 l iiullen, p.s.i 28. 5 25 33. 8 28 38. 8 32 38. 5 37 50.4 55

ear;

OD 68 58 100 68 110 75 140 120 Fold:

Ink No., minutes. 12 10 11 10 10 10 9 10 Pic to 14 15 13 15 13 15 15 15 Porosity No 18 17 20 20 19 24 27 32 Opacity, 13 & L 93 94 94. 8 94 94. s 94 97. 5 95 Brightness, percent G.E 90. 5 90 90. 1 90 90. 6 90 80. 4 90 smoothness, 210 230 231 230 201 230 206 230 Shefi'leld 215 230 232 230 217 230 224 230 'rioi lbs/ton 135 275 105 175 29 60 50 :Hydrgfl (1b )(pulper) 200 200 200 200 225 225 225 225 Size pickup, lbs/ton 340 15 144 130 T10 pickup from size, lbs/ton 42. 5 19 18 13. 7

Run size, tons 4 8. 5 7 7. 5

1 None.

VI.-Following the procedure of Examples I-V, 50 lb. Government Offset of 79 percent G.E. brightness, 91 percent (B&L) opacity was produced by conventional and the new techniques. The former required 154 lbs/ton TiO and the latter, using a pigmented sizing paste produced according to the method of Example A, required a total of 65.2 lbs./ ton TiO Furnish Conventional: New 60% sulfite percent 60 40% kraft do 40 240 lbs/ton clay lbs./ton 242 50 lbs/ton asbestos do 50 lbs/ton TiO [d]beater do 25 127 lbs/ton TiO [s]slurry do Size Conventional:

8% oxidized starch 120-140 lbs/ton pickup (est.) New parts: 1

100 hydrafine clay 20 TiO (micronized anatase) 95 hydroxyethyl starch 190 oxidized starch 1 Applied as 12.8% solids paste with a pickup (Itotal solids) of 206 lbs/ton; 10.2 lbs. T60 51 lbs. clay/ton.

VII.Following the procedure of the preceding examples, using a total of 40.3 lbs/ton TiO 50 lb. Government Offset with 90 percent opacity and 81 percent brightness, which previously required 130 lbs./ ton TiO in the furnish when conventionally sized with 8 percent oxidized starch paste, was produced from the same furnish, except the TiO in the furnish was reduced to 30 lbs./ton and the sheet was sized with the following sizing paste, produced according to the method of Example A.

Furnish:

50% sulfite 37.5 kraft 2.5% refined kraft 10% broke 240 lbs./ ton clay 50 lbs./ ton asbestos 30 lbs/ton TiO Speed: 1150 f.p.rn. Size: 1

100 parts hydrafine clay 20 parts Ti0 A-WD 95 parts Penford 280 192 parts 5592 gum Pickup: 206 lbs/ton Applled as 12.8% solids (19.8 cps/150 E; pH 6.8).

The properties of the paper were as follows:

VIII.Fol1oWing the above procedures, using pigmented sizing paste produced according to the method of Example A, 50 lb. Offset bond with 92 opacity, 89 brightness and 15 pick target specifications was produced from the following furnish and size, employing a total of 157.7 lbs/ton T102.

Furnish:

60% sulfite 40% kraft 45 lbs./ beater alum 18.4 lbs./ ton rosin 50 lbs./ beater hydral 54 lbs./ ton clay 136 lbs./t0n TiO [S] Speed: 530 f.p.m. Size: 1

parts Hydral SD. 20 parts TiO [M] 50 parts Delta Gum 7424 50 parts Penford 280 Pickup: 217 lbs/ton 1 Applied as 20.6% solids (4'3 cps/ 11, pH 6.2). The properties of the paper were as follows:

New Target Basis wt. lbs., 25 38l500 50. 5 50 Caliper, in. 10- 39 40 Mullen, p.s.i 25. 3 25 Teai r 51 46 CD 47 46 Ink penetration, minutes 13 10 Pick, top 15 15 Porosity, sec 22 14 Opacity, percent 91. 1 92 Brightness, percent G.P 88. 7 89 smoothness, W 225 230 Shefiield, T 222 230 Ash, percent 16. 61

1X.Following the above procedure, 50 lb. offset bond with 89% brightness was produced using pigmented size produced according to the procedure of Example A.

Furnish:

60% sulfite 40% kraft 40 lbs/ton (pulper) alum 13.9 lbs/ton rosin 177 lbs/ton TiO [S] 100 lbs/ton (pulper) Hydral Speed: 520 f.p.m. Size: 1

50 parts Ultra White 90 25 parts Hydral SD. 25 parts TiO [M] 50 parts Penford 230 50 parts Pearl X Pickup: 241 lbs/ton Applied as 19.5% solids (97.8 cps/150 F.; pH 0.4).

The properties of the paper were as follows:

New Target Basis wt. lbs., 25)(38/500 50. 3 50 Caliper, in. 40 40 Mullen, p.s.i 28. 1 25 Tear:

Ink No., minutes 19 10 Porosity, sec 17 14 Opacity, percent 90. 5 02 Brightness, percent 00. 3 80 smoothness, W 228 230 Ash, percent 15. 6

X.In this run, the objective was to increase the opacity of 11 lb. (17 light weight Register Bond which when produced by conventional techniques, has an opacity of 67-71 percent. The size paste was prepared according to Example A.

40 parts hydragloss clay 40 parts hydrafine clay parts TiO [M] 100 parts hydroxyethyl starch 1 Applied as 17.6% solids, 103 lbs/ton pickup.

The opacity of the paper produced by the new technique was 75-77 percent. To increase the opacity of the conventional paper to 75-77 would require at least 100 lbs/ton additional, i.e., 129 lbs/ton total, TiO i.c., 57 lbs/ton more than that required by the new technique By the new technique, the opacity of the paper was increased 6 points, from 69-71 to 75-77, using only 43 lbs/ton additional TiO Xl.In this run, using size prepared according to the procedure of Example A, high opacity 11 lb. (l7

v light weight smooth finish bright bond was produced by the new technique from the following furnish and size.

the furnish than would otherwise have been required 2 Applied as 17.6% solids (250 cps/150 F.; pH 6.0).

Properties New Target Basis wt. lbs. 17X22/500. 11.5 11.0 Caliper, in. 102 21 Mullen, p.s.i 18. 6 16 Ink N0., minutes 1, 3 Pick, top 17 12 Porosity, sec 2t) Opacity, percent 75. 5 smoothness, W 83 Sheilieltl, T. 83 80 Ash, percent What is claimed is:

1. A method for producing a titanium dioxide-containing, size press coated, printing grade paper, having a high ratio of base sheet opacity increase to amount of titanium dioxide employed to achieve such increase, which comprises the steps of:

(a) forming a furnish containing substantially less titanium dioxide than conventionally employed to achieve the target opacity for the grade and weight paper to be produced from the furnish;

(b) forming a sizing paste comprising starch and a stable suspension of titanium dioxide therein produced by cooking an aqueous mixture comprising starch and titanium dioxide with steam at a temperature above 212 F. while subjecting the mixture to mechanical energy in excess of that provided by the steam required to cook the mixture at the selected temperature which is sufficient to break up agglomerates of the pigment particles and form a uniform dispersion in which the titanium dioxide particles are dispersed in a finely dispersed particulate condition, substantially free from agglomerates present when titanium dioxide and the sizing material are blended in a conventional manner;

(0) forming a web of the furnish with a base sheet opacity at least one point (B&L) less than the target opacity;

(d) at least partially drying the formed Web;

(e) size press coating the formed, at least partially dried web with the sizing paste produced in step (b) in an amount which, with the titanium dioxide, if any, supplied to the furnish, is substantially less than the total amount of titanium dioxide conventionally required to produce uncoated and size coated paper of the same grade and weight with comparable opacity; and

(f) drying the size press coated paper.

2. A method according to claim 1 wherein the sizecoated paper thus produced is printing grade paper having an opacity of at least (B&L) and the amount of titanium dioxide employed in the furnish is less than lbs/ton and the amount applied by the size coating is less than 50 lbs/ton.

3. A method according to claim 2 wherein the paper produced is untinted paper of less than 80 lb. (25 X weight, the furnish contains less than half the titanium dioxide conventionally employed to produce paper of that grade, weight and opacity, and the amount of titanium dioxide applied by the size coating is from about 10 to about 30 lbs./ton.

4. A method according to claim 3 wherein the paper is less than 60 lb. (25 weight and has a brightness and opacity of at least 90 each. i

5. A method according to claim 1 wherein both the furnish and the size paste contain titanium dioxide and at least one thereof contains another pigment.

6. A method according to claim 5 wherein the furnish contains up, to 150 lbs/ton of titanium dioxide and the solids in the sizing mix contain up to 15 percent titanium dioxide andjat least one of the furnish and sizing mix contains alumina. ,;l

7. Size press coated, printing grade paper having an opacity of at least 90, at least three points of which are provided by a titanium dioxide containing s'ize press coating containing up to 50 lbs./ ton of titanium dioxide, produced according to the process of claim 1.

8. Untinted paper of less than 80 lb. (X %oo) weight, having a brightness of at least 90, at least seven points of its opacity being provided by a titanium dioxide containingsize press coating providing 10 to lbs/ton titanium dioxide, produced according to the process of claim 1.

References Cited UNITED STATES PATENTS s. LEON BASHQRE, Primary Examiner R. H. ANDERSQN, Assistant Examiner US. 01. X.R. 

